The present invention relates generally to a multiplex system, and, more particularly, to a time division multiplex system for motor vehicles and other applications.
Motor vehicles have traditionally used conventional point-to-point wiring systems to provide power to and to control or monitor the operation of various equipment positioned throughout the vehicle. In recent years, however, tremendous demands have been placed on the wiring systems of boats, rv's, and other vehicles due to the numerous safety devices that are now required and the many amenities that are now available and that consumers desire in their vehicles. The increase in the size and complexity of vehicular wiring systems necessitated by this additional equipment has resulted in wiring systems which occupy excessive space in the vehicle, and which are costly to manufacture and difficult to service.
One proposed solution to the problem of the increasing complexity of conventional, vehicle-wiring systems is the use of a multiplex system. Multiplexing is a technique commonly used in the electronics arts to send two or more messages on the same wire and, in essence, permits many of the wires in a traditional vehicle wiring system to be replaced by electronics, thus reducing the complexity and space requirements of the wiring.
One form of multiplexing that has been proposed for vehicle applications is time division multiplexing in which a plurality of different signals is transmitted over a line in cyclical fashion and a plurality of receivers is connected to the line and is responsive to the signals to control vehicle components coupled to the receivers.
In some known multiplex systems, a single central transmitter generates a train of pulses which are encoded using, for example, pulse width or pulse amplitude modulation techniques. Each receiver is responsive to a particular pulse in the train and decodes the pulse to determine whether or not its associated load should be activated. In other known systems, a plurality of transmitter-receiver pairs is connected to a communication line, and each transmitter transmits a data signal over the line which is adapted to be received by its associated receiver to control a load coupled to the receiver. In such systems, each transmitter-receiver pair is typically allotted a particular time channel to transmit signals over the line.
Many vehicle multiplex systems include two or more wires or busses to transmit power, data, and timing signals through the system. Such systems tend to be costly to manufacture and difficult to service, particularly in the field. Other systems require only a single wire to carry power, timing, and data signals through the system; however, these systems are often complex in design and tend to be limited in their capabilities.